[0:01]Now we're going to talk about the respiratory system, whose goal ultimately is to achieve gas exchange with the blood. But there are many important structures that move and modify air before it gets to that point.
[0:18]So, we're going to start by talking about the structure and function of the nasal cavity before moving a little bit deeper down to talk about the larynx. Then once we get into the chest cavity, we're going to be talking about the trachea, bronchi, hilum, and the major blood vessels that supply the lungs. We're going to talk about the wrappings of the lung and the chest cavity called the pleura. We're going to talk about superficial anatomy of the lungs as well as bony thorax that incases the lungs. And then finally, we're going to talk about the major muscle of respiration, which is the diaphragm and the nerve that innervates it, which is the phrenic nerve. The respiratory tract itself can be divided into an upper and lower portion. The upper portion consists of nasal sinuses, nose, the nasal cavity, a shared oral, digestive, and respiratory space called the pharynx, and then the larynx. After which, we have the lower respiratory tract starting with the trachea that divides into bronchi to supply the lungs. We're going to focus first on the upper respiratory tract. In particular, we're going to start with the nose and nasal cavity. In this anterior view of a skull, we see that the anterior most portion of the nose isn't actually made up of bone, but it's made up of cartilage, what makes it very flexible and very movable. Further back, we do have bone that's connected to the rest of the skull. If we were to take off that cartilage and look into the nasal cavity itself, we'd see that there's a wall at this point made up of bone called the septum that divides the cavity into left and right cavities. We also notice that laterally on each nasal cavity wall, we have these weird shaped bones called nasal concha or turbinates that have that shape to help achieve their very important functions. Now, let's look at a sagittal view right down the midline. And we're going to look towards the septum from the left side. anteriorly, it's again made up of cartilage, which gives it the flexibility that you're probably familiar with with the external nose. But further back, it's made up of bone, so it's rigid. Now, if we were to take a coronal section somewhere around this bony septum, we see there's actually a lot of spaces here. So we again find the bony septum in the midline separating the cavity into left and right. And we again see these weird shaped bones coming off of the lateral wall, the concha or turbinates. We see that they're named for their location. We have a superior, a middle, and an inferior nasal concha on either side. We also notice surrounding the nasal cavity, these spaces within the bone called sinuses. And they're lined by mucous membranes that are made up of the same type of epithelium as the rest of the nasal cavity. And their function is somewhat unknown, we don't really know, there are a lot of theories, for example, these spaces help make the head lighter. Um, they add resonance to the voice.
[3:47]Regardless of what they're really doing there, they are important because they are connected to these nasal cavities, and therefore, infections, for example, can spread into them and cause inflammation or sinusitis. Let's go back to this midline lateral view where we again see the nasal septum, this time in pink because we've covered it with some mucosa. If we were to take away that septum by moving just a little bit to the right of midline. And again, taking it from this view from the left, we will now see the right lateral wall of the nasal cavity. Now, we can see these Conca or turbinates. We see the superior, the middle, and the inferior nasal turbinate here. And there's a lot of functions to these turbinates. For example, the air we breathe in is fairly dry and it's fairly cold compared to the rest of the body. And they actually create turbulence in conjunction with the mucosa that lines these, helps to warm the air, humidify it, and help clean it. It also helps to direct air upwards to the top of the nasal cavity, where we have a special type of mucosa called olfactory mucosa. And all factory means smelling. So, this area is a specialized area for smell. And in fact, in this area, there are a bunch of tiny nerves that collectively make up the first cranial nerve or olfactory nerve, which is the nerve of smelling. And these tiny little nerves pass through the skull at this area to reach the cranial cavity at a special spot called the old factory bulb. Which will then have a tract that goes back to the brain to process the sense of smell. Let's look at a bit of a complicated issue here when we talk about breathing and eating. So we just talked about air moving through the nasal cavities, and its objective is to ultimately get down into the lungs. However, we also have an oral cavity through which things like food and water are going to pass, eventually back to the esophagus and into the stomach. But this creates a problem because as you can see, there's a space where both food and water are shared with air. And so, how do we prevent things like food and water from ending up in the lungs and essentially choking us? So let's look what happens when we try to swallow a portion of food. When we've chewed up a bit of food, it forms something called a bolus. And it's held in place here by the tongue. If we look posterior to this, we see that there's an area of the palate that lacks bone. And that's the soft palate. And more inferiorly, at the base of the tongue, we have this little flap of tissue called the epiglottis. During the act of swallowing, the tongue and several other muscles push this bolus back posteriorly. And the soft palate acts as a flap to prevent food from going up into the nasal cavity, while the epiglottis serves to flap down and protect the opening to the airway. As food is being swallowed, therefore, it forces food posteriorly and back into the esophagus where it belongs.
[8:16]Now, let's move down a little bit further and talk about the larynx. Here we have a nice sagittal view that's zoomed in a little bit here so we could see just a little bit of the base of the tongue here. So this is the most posterior, inferior portion of the tongue.
[8:48]We also see a unique bone in the neck called the hyoid bone.
[8:58]And we see that flap of tissue that helps move food posteriorly into the esophagus, therefore protecting our airway, which was the epiglottis. And from here, we're going to start seeing the larynx.
[9:25]A little bit further down, we have a fold called the vestibular fold. And just below that, we have something called the vocal fold. As you might guess by the name, the vocal fold is actually what's going to help create vocalization or speech.
[9:55]And then beyond the larynx, we finally have the lower respiratory tract starting with the trachea. And again, posterior to the trachea is going to be the esophagus on its way down to the stomach. Here we have a view from posterior where we've opened up the larynx to look towards it so we could actually see all of the epiglottis here. As this little flap that will come down and protect the airway. And as we go down a little bit, we see both of these folds that we called vestibular folds. We also call them false vocal cords because they look very similar in location at least to the vocal cords.
